Personality traits, sex and food abundance shape space use in an arboreal mammal

Captive-raised western ringtail possum (Pseudocheirus occidentalis) with a bold personality have higher survival rates when released into the wild

We tested if the personality of captive-raised western ringtail possums (Pseudocheirus occidentalis), and the impact of other variables would influence their survival after release using radiotelemetry. We hypothesised a greater survival for individuals: (i) bold; (ii) habituated in advance to food collected from the release area; (iii) juveniles instead of adults, because more easily tolerated by wild individuals, and (iv) released in new dreys (nests) as they would not have the strong odour of old dreys and would be less attractive to foxes. After 3 months of radio tracking, out of 143 possums released, 79 died: 51 (64.6%) were preyed upon by European red foxes (Vulpes vulpes). Bold or female individuals had higher survival rates than shy or male individuals (survival rate bold: 53%, shy: 41%, p = 0.046, hazard ratio = 0.352, 95% CI HR [0.126, 0.979]; survival rate females: 44%, males: 35%, p = 0.007, hazard ratio = 2.811, 95% CI HR [1.322, 5.976]). Shooting was a more effective fox control strategy to improve survival compared to baiting (p = 0.019, hazard ratio = 0.167, 95% CI HR [0.038, 0.742]). Our results demonstrate that the control of introduced predators is critical for the success of reintroductions of this critically endangered species.

Impact of Personality Trait Interactions on Foraging and Growth in Native and Invasive Turtles

Animal personalities play a crucial role in invasion dynamics. During the invasion process, the behavioral strategies of native species vary among personalities, just as the invasive species exhibit variations in behavior strategies across personalities. However, the impact of personality interactions between native species and invasive species on behavior and growth are rarely illustrated. The red-eared slider turtle (Trachemys scripta elegans) is one of the worst invasive species in the world, threatening the ecology and fitness of many freshwater turtles globally. The Chinese pond turtle (Mauremys reevesii) is one of the freshwater turtles most threatened by T. scripta elegans in China. In this study, we used T. scripta elegans and M. reevesii to investigate how the personality combinations of native and invasive turtles would impact the foraging strategy and growth of both species during the invasion process. We found that M. reevesii exhibited bolder and more exploratory personalities than T. scripta elegans. The foraging strategy of M. reevesii was mainly affected by the personality of T. scripta elegans, while the foraging strategy of T. scripta elegans was influenced by both their own personality and personalities of M. reevesii. Additionally, we did not find that the personality combination would affect the growth of either T. scripta elegans or M. reevesii. Differences in foraging strategy may be due to the dominance of invasive species and variations in the superficial exploration and thorough exploitation foraging strategies related to personalities. The lack of difference in growth may be due to the energy allocation trade-offs between personalities or be masked by the slow growth rate of turtles. Overall, our results reveal the mechanisms of personality interaction effects on the short-term foraging strategies of both native and invasive species during the invasion process. They provide empirical evidence to understand the effects of personality on invasion dynamics, which is beneficial for enhancing comprehension understanding of the personality effects on ecological interactions and invasion biology.

Predation can shape the cascade interplay between heterothermy, exploration and maintenance metabolism under high food availability

Maintenance metabolism as the minimum energy expenditure needed to maintain homeothermy (a high and stable body temperature, T b), reflects the magnitude of metabolic machinery and the associated costs of self-maintenance in endotherms (organisms able to produce heat endogenously). Therefore, it can interact with most, if not all, organismal functions, including the behavior-fitness linkage. Many endothermic animals can avoid the costs of maintaining homeothermy and temporally reduce T b and metabolism by entering heterothermic states like torpor, the most effective energy-saving strategy. Variations in BMR, behavior, and torpor use are considered to be shaped by food resources, but those conclusions are based on research studying these traits in isolation. We tested the effect of ecological contexts (food availability and predation risk) on the interplay between the maintenance costs of homeothermy, heterothermy, and exploration in a wild mammal-the yellow-necked mouse. We measured maintenance metabolism as basal metabolic rate (BMR) using respirometry, distance moved (exploration) in the open-field test, and variation in T b (heterothermy) during short-term fasting in animals captured at different locations of known natural food availability and predator presence, and with or without supplementary food resources. We found that in winter, heterothermy and exploration (but not BMR) negatively correlated with natural food availability (determined in autumn). Supplementary feeding increased mouse density, predation risk and finally had a positive effect on heterothermy (but not on BMR or exploration). The path analysis testing plausible causal relationships between the studied traits indicated that elevated predation risk increased heterothermy, which in turn negatively affected exploration, which positively correlated with BMR. Our study indicates that adaptive heterothermy is a compensation strategy for balancing the energy budget in endothermic animals experiencing low natural food availability. This study also suggests that under environmental challenges like increased predation risk, the use of an effective energy-saving strategy predicts behavioral expression better than self-maintenance costs under homeothermy.

Boldness suppresses hoarding behavior in food hoarding season and reduces over-wintering survival in a social rodent

The "pace-of-life" syndrome (POLS) framework can encompass multiple personality axes that drive important functional behaviors (e.g., foraging behavior) and that co-vary with multiple life history traits. Food hoarding is an adaptive behavior important for an animal's ability to adapt to seasonal fluctuations in food availability. However, the empirical evidence for the relationships between animal personality and hoarding behavior remains unclear, including its fitness consequences in the POLS framework. In this study, the Mongolian gerbil (Meriones unguiculatus), a social rodent, was used as a model system to investigate how boldness or shyness is associated with food hoarding strategies during the food hoarding season and their impact on over-winter survival and reproduction at both individual and group levels. The results of this study showed that, compared with shy gerbils, bold gerbils had a lower effort foraging strategy during the food hoarding season and exhibited lower over-winter survival rates. However, bold-shy personality differences had no effect on over-winter reproduction. These findings suggest that the personality is a crucial factor influencing the foraging strategy during the food hoarding season in Mongolian gerbils. Personality may be related to energy states or the reaction to environmental changes (e.g., predation risk and food availability) in bold or shy social animals. These results reflect animal life history trade-offs between current versus future reproduction and reproduction versus self-maintenance, thereby helping Mongolian gerbils in adapting to seasonal fluctuations in their habitat.

Lovers, not fighters: docility influences reproductive fitness, but not survival, in male Cape ground squirrels, Xerus inauris

Over their lifetime, individuals may use different behavioural strategies to maximize their fitness. Some behavioural traits may be consistent among individuals over time (i.e., 'personality' traits) resulting in an individual behavioural phenotype with different associated costs and benefits. Understanding how behavioural traits are linked to lifetime fitness requires tracking individuals over their lifetime. Here, we leverage a long-term study on a multi-year living species (maximum lifespan ~ 10 years) to examine how docility (an individual's reaction to trapping and handling) may contribute to how males are able to maximize their lifetime fitness. Cape ground squirrels are burrowing mammals that live in social groups, and although males lack physical aggression and territoriality, they vary in docility. Males face high predation risk and high reproductive competition and employ either of two reproductive tactics ('natal' or 'band') which are not associated with different docility personalities. We found that although more docile individuals sired more offspring on an annual basis, docility did not affect an individual's long-term (lifetime) reproductive output. Survival was not associated with docility or body condition, but annual survival was influenced by rainfall. Our findings suggest that although docility may represent a behavioural strategy to maximize fitness by possibly playing a role in female-male associations or female mate-choice, variations in docility within our study population is likely maintained by other environmental drivers. However, individual variations in behaviours may still contribute as part of the 'tool kit' individuals use to maximize their lifetime fitness.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00265-023-03421-8.

Animal-friendly behavioral testing in field studies: examples from ground squirrels

Field studies of behavior provide insight into the expression of behavior in its natural ecological context and can serve as an important complement to behavioral studies conducted in the lab under controlled conditions. In addition to naturalistic observations, behavioral testing can be an important component of field studies of behavior. This mini review evaluates a sample of behavioral testing methods in field studies to identify ways in which behavioral testing can be animal-friendly and generate ethologically relevant data. Specific examples, primarily from studies of ground squirrels, are presented to illustrate ways in which principles of animal-friendly behavioral testing can be applied to and guide testing methods. Tests conducted with animals in their natural habitat and that elicit naturally occurring behavioral responses can minimize stress and disturbance for animals, as well as disruption of the larger ecosystem, and can have high ethological validity. When animals are trapped or handled as part of a study, behavioral testing can be incorporated into handling procedures to reduce overall disturbance. When behavior is evaluated in a testing arena, the arena can be designed to resemble natural conditions to increase the ethological relevance of the test. Efforts to minimize time spent in testing arenas can also reduce disturbance to animals. Adapting a behavioral test to a species or habitat conditions can facilitate reduced disruption to subjects and increased ethological relevance of the test.

Multiple benefits of juvenile play: A ground squirrel's perspective

Adaptive functions of play can vary across species, and also within species, reflecting behavioral ecology and evolutionary history. We evaluated juvenile play in Belding's ground squirrels (Urocitellus beldingi), a species for which field studies have assessed play behavior in the context of the squirrels' ecology and life history. Social play behavior in U. beldingi appears not to have the range of adaptive benefits related to social behavior apparent in species with more complex social organization. Play in juvenile U. beldingi improves general motor skill, which may translate to more proficient performance of behaviors during and beyond the juvenile period. Social play in juvenile squirrels is associated with refinement of temperament and behavior, promoting behavioral shifts toward less docile responses as well as more cautious behavior. Social play also influences behavior of juvenile squirrels in novel situations, fostering greater exploration and adaptability of responses. Important life events in U. beldingi such as the timing of natal dispersal and defense of maternal territories can be influenced by juvenile play.

Pet cat personality linked to owner-reported predation frequency

The domestic cat, Felis catus, is one of the most popular and widespread domestic animals. Because domestic cats can reach high population densities and retain at least some tendency to hunt, their overall impact on wildlife can be severe. Domestic cats have highly variable predation rates depending on the availability of prey in their environment, their owners' practices, and individual cat characteristics. Among these characteristics, cat personality has recently been hypothesized to be an important factor contributing to variations in the hunting activity of cats. In this study, we surveyed 2508 cat owners living in France about their cats' personalities, using the Feline Five personality framework, and the frequency with which cats bring home prey. Personality traits were analyzed using factor analysis and related to predation frequency using cumulative logit models. For both birds and small mammals, cats with high levels of extraversion or low levels of neuroticism had significantly higher frequencies of prey return. Owners whose cats had low levels of agreeableness or high levels of dominance reported a significantly lower frequency of bird return. Personality differences therefore seem to contribute to the high variability in predation rates among domestic cats. We also found that the owner-reported prey return frequencies were significantly higher for cats spending more time outdoors, for non-pedigree cats, and for owners living in rural or suburban areas as opposed to urban areas. By contrast, we did not detect an effect of cat sex or age on their reported prey return rates.

Living on the edge: morphological and behavioral adaptations to a marginal high-elevation habitat in an arboreal mammal

Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species, which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments. We studied three alpine populations of Eurasian red squirrels (Sciurus vulgaris), one living in a marginal high-elevation habitat at the edge of the species' altitudinal distribution, and two occurring in higher-quality habitats. Here, we investigated whether squirrels living in the marginal area differed in two morphological parameters (body size and body mass) and/or in the expression of four personality traits estimated with an open field test and a mirror image stimulation test (activity, exploration, activity-exploration and social tendency). Furthermore, we tested whether within-individual variance of the traits (behavioral plasticity) was higher in the edge habitat. Male squirrels in the edge habitat were smaller and weighed less than in the other study areas, while among females size-habitat relationships were less marked. These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels. Squirrels in the marginal habitat were more active, explorative and had a more social personality than in the other habitats. However, in contrast to our predictions, behavioral plasticity was smaller in the marginal habitat, but only for the trait exploration. Our results suggest that animals choose the habitat that best fits their personality, and that habitat-related differences in selective pressures may shape animals' morphology. This article is protected by copyright. All rights reserved.

Invasive alien species as an environmental stressor and its effects on coping style in a native competitor, the Eurasian red squirrel

Free-living animals cope with environmental stressors through physiological and behavioural responses. According to the unidimensional model, these responses are integrated within a coping style: proactive individuals (bold, active-explorative and social) have a lower hypothalamic-pituitary-adrenal (HPA) axis reactivity than reactive ones (shy, less active-explorative, less social). These associations may change when individuals are exposed to human-induced rapid environmental change (HIREC), such as the introduction of invasive alien species (IAS). Here, we studied Eurasian red squirrels to investigate the relationship between personality traits and one integrated measure of HPA axis activity, both in areas uncolonized (natural populations) and colonized by an IAS, the Eastern grey squirrel (invaded populations). We expected an association between physiological and behavioural responses, and that activity, exploration and social tendency would covary, forming a behavioural syndrome in natural populations, while competition with the IAS was predicted to disrupt these associations. We used faecal glucocorticoid metabolites (FGMs) as an integrated measure of adrenocortical activity, and measured the levels of four personality traits (exploration, activity, activity-exploration and social tendency) with an open field test and a mirror image stimulation test. We found no correlation between FGMs and personality traits, neither in natural nor invaded populations. However, we found correlations among personality traits in areas without interspecific competition, indicating a behavioural syndrome, which was disrupted in invaded populations. This is one of the few studies showing that an IAS, acting as an environmental stressor, alters a native species' behavioural syndrome, but does not influence its coping style.